Australian police have arrested four men, all Australian citizens of Somali and Lebanese descent, for allegedly plotting to attack a military base in the city of Melbourne.

Over 400 police officers were involved in the search operation of 19 homes across the city early on Tuesday to arrest the suspects, who are accused of planning to stage a guerilla attack on Holsworthy Barracks, a major military installation in western Sydney.

“The alleged offenders were prepared to inflict a sustained attack on military personnel until they themselves were killed,” Tony Negus, acting chief commissioner of the Australian Federal Police, said.

“The men’s intention was to go into these army barracks and to kill as many people as possible…. This would have been, if it had been able to be carried out, the most serious attack on Australian soil,” Negus continued adding that the attack could have been the most serious terrorist attack on Australian soil.

Police claim the men had been under surveillance for seven months. The suspects are Australian nationals of Somali and Lebanese descent aged in their 20s.

Police believe those arrested are linked to Somali’s insurgent group al-Shabab, which is fighting the UN-backed Somali government and is believed to have links to al-Qaeda. The suspects are scheduled to appear in court later in the day.

Australian Prime Minister Kevin Rudd said the arrests offered a “sobering reminder of the enduring threat from terrorism at home, here in Australia, as well as overseas.”